The study on allorecognition in colonial animals

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1. The two species of Japanese sponges, Hilichondria okadai and H.Japonica, showed allorecognition responses. A piece of an individual fused with another piece of the same individual, but did not fuse with the piece of the other individual. This suggests that the genes controlling allorecognition show high polymorphism. On the contrary, the rate of fusion among larvae from a single female individual was very high. In a larva the mechanism of allorecognition might be too immature to reject incompatible larvae.2. Bryozoan colonies showed allorecognition responses. Fusion or destruction of zooeciums was observed along the boundary between two contact colonies.3. It was already reported that botryllid ascidians show the delayd allorecognition responses when two incompatible colonies has fused. This responses are called "colony resorption", and botryllids display a hierarchy of this responses.It becomes clear that the ability of allorecognition is common among colonial invertebrates. However, it is unclear whether the ability of allorecognition has been kept in only colonial animals through their evolution processes or that ability is a common and basic function for all animals. We need much study on the genetics of allorecognition in sponges and bryozoans in order to compare with MHC of vertabrates, and also need examination of many animals of other phylum about the presence of allorecognition.